To provide a device for measuring the wall thickness of a pipe, capable of accurately measuring the wall thickness of the pipe, by removing the distortions due to heating among the distortions occurring on the pipe surface.

A pressure detector 17 detects the internal pressure of a pipe. A distortion detecting device 15 detects the circumferential and axial distortions on the pipe surface. A temperature detector 11 detects the temperature of the pipe. A Young's modulus calculation means 13 calculates the Young's modulus of a pipe material from the pipe temperature detected by the temperature detector 11; an internal pressure distortion calculation means 16 calculates the circumferential and the axial distortions on the pipe surface due to the internal pressure of the pipe, by removing the distortions due to heat from the circumferential and axial distortions on the pipe surface detected by the distortion detecting device 15; a wall thickness calculating means 14 calculates the wall thickness of the pipe, based on the internal pressure of the pipe detected by the pressure detector 17; the circumferential or axial distortion on the pipe surface due to the internal pressure of the pipe calculated by the internal pressure distortion detector 16; and the Young's modulus of the pipe material calculated by the Young's modulus calculation means 13.